Topic: Questions on #1 carb off '78 750k

[climbingaz]

Going through the arduous task of cleaning and rebuilding the carbs on my newly aquired '78 CB750K (which had been sitting for 15 years!!) and have a few questions regarding the #1 carb.

First question:

In picture 1, I think I'm pointing at the "SLOW JET" which is apparently clogged up because neither a shot of compressed air or carb cleaner produces any flow anywhere else in the carb.  In the service manual is says to remove and clean the slow jet, but I can't figure out how to remove it.  Is it just pushed into the body of the carb?  Do you have to unscrew it or does it just pop in and out?

Second question:

In pictures 2 and 3, I'm pointing to one of the inlets/outlets that goes from outside of the carb to a recessed "cup" inside the carb.  On carbs #2 and #3 this passage is free (allows a flow of air) when I shoot compressed air but seems to be blocked on the #1 carb.  On the #4 carb it isn’t even there.  I'm thinking it's meant to be blocked, because no amount of cleaning or poking produces any dirt or gunk.  Does this make sense?  It's on the outside of the #1 carb.

[GammaFlat]

You're right about the slow jet.  You need to "pull" it out.  Use your favorite pliers or similar tool to work it out.  There are no threads on 77/78 K carbs (for the slow jet).  Once out, you can clean.  Be cautious to not change the size of the hole of the jet when you "clear" the passage-way. 

[climbingaz]

You're right about the slow jet.  You need to "pull" it out.  Use your favorite pliers or similar tool to work it out.  There are no threads on 77/78 K carbs (for the slow jet).  Once out, you can clean.  Be cautious to not change the size of the hole of the jet when you "clear" the passage-way. 

Thanks!  Any thoughts about my second question?

[Spanner 1]

Yep, it's a vent for the float bowl and only on 2+3 carbs...not sure why...anyone else ? Should have lines connected that go over the air box....

[MrHellpop]

You're right about the slow jet.  You need to "pull" it out.  Use your favorite pliers or similar tool to work it out.  There are no threads on 77/78 K carbs (for the slow jet).  Once out, you can clean.  Be cautious to not change the size of the hole of the jet when you "clear" the passage-way. 

yes, be careful not to enlarge the hole. I'm not exactly sure how one would do that on accident though, unless you are using a drill to clean it! I have a 77 ( same carbs as the 78 I believe) and after removing and cleaning by soaking in simple green and blowing out with carb cleaner, I looked through them and noticed that one of them had a significantly larger diameter than the other 3. I resoaked and blew out one a few more times, (and also poked a thin sewing needle thru to make sure the path was cleared) all of which enlarged the diameter correctly. no, I am not saying to use a sewing needle to 'carve out' the jets! The needle fit into the cleaned jet I had, but wouldn't in the others until I had thouroghly recleaned them. All of this is a really long winded way of me saying: these are hard to really clean, and you should make sure they are actually cleaned all the way! Before pulling and cleaning these guys, my bike would not idle without the choke on, no matter how warm the engine got. Now it idles and runs like a champ!
Good luck!

[Gordon]

Yep, it's a vent for the float bowl and only on 2+3 carbs...not sure why...anyone else ? Should have lines connected that go over the air box....

There's a tube that connects 2 & 3 carb vents to 1 & 4 so they're all at ambient air pressure inside the bowls.  They didn't make separate molds for each individual carb based on where it was going to be on the rack, so all carbs have two places for bowl vents even though only the inner two carbs actually use both of them.  They just left the outer vent ports undrilled on 1 & 4.  It's one of those money-saving efficiencies that Honda employed.  Sort of like the extra ground wire behind the left side panel on our U.S. model bikes. 

[climbingaz]

I've only been on the board for a few months now, but am thoroughly IMPRESSED by how helpful and knowledgeable everyone has been!

THANKS